1. Field of the Invention
The present invention relates to an electrical apparatus, a control device and a communication method.
2. Description of the Related Art
FIG. 9 illustrates a configuration of a conventional electrical apparatus 1. The electrical apparatus 1 includes a main controller (a control section 2 equipped with a main CPU) that performs primary control within the electrical apparatus 1; and a plurality of devices 3, 4, 5 and so on that individually communicate with the control section 2. The communications between the devices 3, 4, 5 and so on and the control section 2 are performed at different communication rates (e.g., the communication rates of the devices 3 and 4 are X bps and Y bps, respectively) and in conformity with different communication schemes (e.g., the communication scheme of the devices 3 and 4 is A; the communication scheme of the device 5 is B). The control section 2 has ports a1, a2, b1 and b2. Specifically, the ports a1 and a2 are used to communicate with the devices 3 and 4 in conformity with the communication scheme A; the ports b1 and b2 are used to communicate with the device 5 in conformity with the communication scheme B. In this case, in order to prevent the communication between the control section 2 and an arbitrary one of the devices from causing an improper operation of another device, it is necessary to use a switch SW to switch between the respective communication lines that connect the control section 2 to the devices 3, 4, 5 and so on (a circuit configuration that performs the switching operation and a process of controlling the switching of the switch SW by the control section 2 are required).
On the other hand, a known control device is configured to conduct serial communications between a primary control section and a plurality of terminal control sections by using a signal line. More specifically, the primary control section can communicate with the terminal control sections at different communication rates; a low communication rate and a high communication rate, the high communication rate being an even number of times as high as the low communication rate. When the communication is conducted at the high communication rate, the data bit coming immediately after the start bit is fixed to High, thereby enabling the communications at the high and low communication rates to be discriminated between each other (see JP 2000-172908 A).
When a control section and devices are mounted on respective independent boards in an electrical apparatus, the inner space of the electrical apparatus and the total size of the boards are requested to be reduced as much as possible by decreasing the number of communication lines that connect the boards and the number of components required for this connection. Likewise, even when a control section and devices are mounted on a single board, the inner space of the electrical apparatus and the size of the board are also requested to be reduced by decreasing the number of communication lines that connect them and associated components. Moreover, in some cases, a debugging connector to which an external debugging jig is to be connected is provided at a site of the housing of the electrical apparatus. If the control section is connected to the devices by respective independent communication lines, a plurality of debugging connectors need to be provided in accordance with the number of communication lines. However, in order to carry out debugging work efficiently, decrease the number of components, and improve the appearance, for example, using a minimal number of debugging connectors is preferred.
In the light of the above requests, it can be said that a preferable configuration of the electrical apparatus 1 is that a single common communication line is used for the communications between the control section 2 and the devices 3, 4, 5 and so on and that the switch SW not be used. However, use of the single common communication line, which involves not using the switch SW, may cause improper operations of the devices as described above. For this reason, a configuration that enables a single common communication line to be used but assures a proper operation of each device is needed.
In the above control device described in JP 2000-172908, among the terminal control sections that receive data from the primary control section, a normal-speed terminal starts its communication on the condition that the level on an SYN line becomes Low, and a high-speed terminal that conducts a high-speed communication starts its communication on the condition that the data bit coming immediately after the start bit is High. Thus, if the terminal control sections support different communication rates, it is necessary to individually set the communication starting conditions in these terminal control sections. Consequently, an actual configuration of communications between a primary control section and a plurality of terminal control sections may be complicated.